The present invention relates to a friction stir welding method that is especially preferable for welding hollow shape members, and to hollow shape members suitable for such friction stir welding method.
Friction stir welding is a method performed by rotating and inserting a round shaft (called a rotary tool) to a joint region between members to be welded, and moving the same along the joint line, thereby heating, softening, plasticizing, and solid-phase welding the joint region. The rotary tool comprises a large-diameter portion and a small-diameter portion. The small-diameter portion is inserted to the member(s) to be welded, and the end surface of the large-diameter portion is disposed so as to contact the member(s). The small-diameter portion is provided with a screw thread.
Projections protruding to the side from which the rotary tool is inserted are formed to the two members to be welded, and the metal material constituting the projections is used as the source material to fill the gap between the two members. The large-diameter portion of the rotary tool is inserted to the projections.
Since the rotary tool is inserted to the metal material at the abutted region, a great force is added to the joint region. Therefore, upon welding hollow shape members, the area of one hollow shape member where a connecting plate that connects the two face plates exists is selected to be welded with the other hollow shape member. This is because the connecting plates can provide support against the above-mentioned force, thereby preventing deformation of the hollow shape members during the friction stir welding.
The above mentioned prior art method is disclosed in Japanese Patent Laid-Open Publication Nos. 9-309164 (309164/97, EP 0797043A2), and 11-90655 (90655/99, U.S. Pat. No. 6,050,474).
When welding (or friction stir welding) the joint region between two abutted plates, the plates are deformed by the weld heat. One example of such deformation is the deformation in the thickness direction of the plates. Such deformation may cause unevenness between one plate and the other plate being welded, deteriorating the flatness of the plate surface. Therefore, in welding hollow shape members, the members being welded is equipped with a connecting plate that connects the two parallel face plates positioned near the joint region to be welded, thus preventing the face plates from deforming in the thickness direction. Such connecting plate is positioned near the weld region of each hollow member. The connecting plate is orthogonal to the face plates.
The welding temperature of the friction stir weld is low compared to arc welding, so there is less fear of deformation, but deformation still occurs. Therefore, connecting plates are provided to the weld region according to the above-mentioned JP Laid-Open Publications No. 309164/97 (EP 0797043A2) and No. 90655/99 (U.S. Pat. No. 6,050,474). According to the disclosure of 90655/99 (U.S. Pat. No. 6,050,474), each of the hollow shape members being welded are provided with a connecting plate positioned at the end region thereof. Though the connecting plates are required to provide necessary strength to the hollow shape members, the connecting plates also inevitably increase the mass of the members.
In 309164/97 (EP 0797043A2), only one of the two hollow shape members being friction stir welded is provided with the connecting plate.
The object of the present invention is to provide a friction stir welding method that realizes a good weld with a light-weight member, and a hollow shape member used for such method.
The first method for achieving the objects of the present invention characterizes in that an end portion in the width direction of a first hollow shape member is abutted against an end portion in the width direction of a second hollow shape member; the first hollow shape member comprises two face plates; a first connecting plate for connecting the two plates, at least one end of which is connected to a region other than the end portion; a second connecting plate for connecting the end portions of the face plates that is disposed substantially orthogonal to the face plates; recessed portions formed respectively to connecting portions where the two face plates are each connected with the second connecting plate, each recessed portion opening outward toward both the width direction and the thickness direction of the hollow shape member; a groove or projection formed to one recessed portion; and a groove or projection formed to the other recessed portion; the second hollow shape member comprises two face plates; a first connecting plate for connecting the two plates, at least one end of which is connected to a region other than the end portion; a projection or groove formed to one face plate at the end portion of the hollow member; and a projection or groove formed to the other face plate at the end portion of the hollow member; the projections are each inserted to a corresponding groove, respectively, when the two hollow members are abutted against each other, at which time one hollow shape member is inserted to the other hollow shape member so as to substantially suppress movement of the hollow shape member in the thickness direction; and a rotary tool is disposed on the extension of plate thickness of the second connecting plate, thereby friction stir welding the abutted region from the outer direction of thickness of the hollow shape members.
The second method for achieving the objects of the present invention characterizes in that an end portion in the width direction of a first hollow shape member is abutted against an end portion in the width direction of a second hollow shape member; the first hollow shape member comprises two face plates; a first connecting plate for connecting the two plates, at least one end of which is connected to a region other than the end portion; a second connecting plate for connecting the end portions of the face plates that is disposed substantially orthogonal to the face plates; recessed portions formed respectively to connecting portions where the two face plates are each connected with the second connecting plate, each recessed portion opening outward toward both the width direction and the thickness direction of the hollow shape member; a groove or projection formed to one recessed portion; and a groove or projection formed to the other recessed portion; the second hollow shape member comprises two face plates; a first connecting plate for connecting the two plates, at least one end of which is connected to a region other than the end portion; one face plate having at the end portion of the hollow shape member either a projection protruding outward to the width direction of the hollow shape member or a groove opening outward to that direction; and the other face plate having at the end portion of the hollow shape member either a projection protruding outward to the width direction of the hollow shape member or a groove opening outward to that direction; the projections are each inserted to a corresponding groove, respectively, when the two hollow members are abutted against each other; and a rotary tool is disposed on the extension of plate thickness of the second connecting plate, thereby friction stir welding the abutted region from the outer direction of thickness of the hollow shape members.
The third method achieving the objects of the present invention characterizes in that an end portion in the width direction of a first hollow shape member is abutted against an end portion in the width direction of a second hollow shape member; the first hollow shape member comprises two face plates, the two plates each having either a groove opening toward the width direction or a projection protruding toward the width direction, formed at one width-direction-end of the first hollow shape member; the second hollow shape member comprises two face plates, the two face plates each having either a projection protruding toward the width direction or a groove opening toward the width direction, formed at onewidth-direction-end of the second hollow shape member; the projections are each inserted to a corresponding groove, respectively, when the two hollow members are abutted against each other; and the friction stir welding is performed to weld said abutted regions, and the grooves and the projections.
Moreover, one hollow shape member for achieving the objects of the present invention comprises two face plates; a first connecting plate for connecting the two face plates, at least one end of which is connected to a region other than an end portion in the width direction of the hollow shape member; a second connecting plate for connecting the end portions of the two face plates, disposed substantially orthogonal to the face plates; recessed portions provided respectively to each of the two connecting portions where the two face plates are connected with the second connecting plate, each recessed portion opening outward toward both the width direction and the thickness direction of the hollow shape member; and either grooves opening toward the outer direction of width or projections protruding toward the outer direction of width formed to the recessed portions, respectively.
The other hollow shape member for achieving the object of the present invention comprises two face plates; a connecting plate for connecting the two face plates, at least one end of which is connected to a position other than an end portion in the width direction of the hollow shape member; either a projection protruding toward or a groove opening toward the outer direction of width of the hollow shape member, provided to the end of a first face plate at the end portion in the width direction of the hollow shape member; and either a projection protruding toward or a groove opening toward the outer direction of width of the hollow shape member, provided to the end of a second face plate at the end portion in the width direction of the hollow shape member.